1. Field of the Invention
The present invention relates generally to thermal spraying and, more specifically, to a masking for an engine block for thermally sprayed coatings and a method of masking engine blocks for thermally sprayed coatings.
2. Description of the Related Art
It is known to thermally spray articles. For example, thermal spraying has been used to provide a friction and wear resistance coating on cylinder bores of aluminum engine blocks. During the thermal spraying process, molten metal droplets are formed and sprayed in a relatively wide spray pattern at very high velocities from a spray nozzle of a thermal spray gun. The spray nozzle is stationed relatively close to a surface of the cylinder bore due to a restricted diameter of conventional cylinder bores (typically four to six inches). The combination of such high velocity and short travel distance will allow a small proportion of the particles to bounce or be deflected from the target surface resulting in over-spray. Such over-spray contaminates adjacent surfaces of the engine block not intended to be coated or such over-spray merely falls free of the engine block as waste material. The adjacent surfaces may be the crankcase chamber and support surfaces for the crankshaft. As a result, adequate masking must be provided to protect the crankcase and head deck of the engine block from errant particles that are generated during the thermal spray operation.
Early masking techniques used resilient or abatable plugs to protect apertures or holes of the components that are being thermally sprayed or painted. However, such plugs are not good for components having restricted access to the apertures and are a detriment when the interior of the apertures must not be penetrated or obscured to allow for proper spraying. Gases have also been used as a masking medium. Gases are blown across the interior side of a folded or curled sheet material to mask such side from a molten bath of metal into which the folded sheet is dipped. However, if such technique were to be used with thermal spraying of internal cavities, such gases would interfere with the thermal spray deposition.
Another technique to prevent over-spray is by masking cylinder bore extremities. An example of such masking is disclosed in U.S. Pat. No. 5,573,814 to Donovan. In this patent, a method of masking one or more extremities of a cylinder bore from internal thermal spraying is disclosed. The method includes the steps of supporting one or more inflatable mask members adjacent an end of the cylinder bore and pressurizing the inflatable mask member to expand and annularly engage the end of the cylinder bore. However, none of these techniques can be effectively used in an automated mass production environment practiced in the automotive industry.
Although the above method of masking for thermally sprayed articles has worked, it is desirable to improve the masking of engine blocks for thermally sprayed coatings. It is also desirable to provide a masking that accommodates all possible engine blocks and mask misalignments, provides adequate sealing and protects a crankcase and head deck of an engine block from thermal spray over-spray. It is further desirable to simplify the masking process for an engine block for spraying a thermally sprayed coating. It is still further desirable to provide a masking for an engine block that facilitates easy evacuation of the over-spray material and that is re-usable.
Accordingly, the present invention is a masking for an engine block to be thermally sprayed with a coating includes a head deck portion adapted to engage a head deck of an engine block to prevent over-spray of a thermally sprayed coating on the head deck. The masking also includes a crankcase portion adapted to be disposed in a crankcase chamber of the engine block and engage a lower end of a cylinder bore cavity of the engine block to prevent over-spray of the thermally sprayed coating into the crankcase chamber.
Also, the present invention is a method of masking an engine block for thermally spraying a coating. The method includes the steps of providing an engine block to be thermally sprayed and providing a head deck masking for masking a head deck of the engine block. The method also includes the steps of providing a crankcase masking for masking a portion of a crankcase chamber of the engine block, disposing the crankcase masking in the crankcase chamber and engaging the crankcase masking with a lower end of a cylinder bore cavity of the engine block. The method further includes the steps of engaging the head deck masking against the head deck of the engine block. The masking prevents over-spray of a coating, that is thermally sprayed on a wall of the cylinder bore cavity of the engine block, from adhering to the head deck and entering the crankcase chamber.
One advantage of the present invention is that a masking for and method of masking an engine block for thermally sprayed coatings is provided. Another advantage of the present invention is that the method and masking protect the crankcase from misalignment and over-spray during thermal spraying. Yet another advantage of the present invention is that the method and masking incorporate high temperature rubber with aluminum. Still another advantage of the present invention is that the masking provides adequate stiffness and sealing in selected areas of the engine block, allowing easy evacuation of the over-spray and preventing hot thermal spray particles from adhering to the engine block during coating operation.
Other features and advantages of the present invention will be readily appreciated, as the same becomes better understood after reading the subsequent description taken in conjunction with the accompanying drawings.